Salt bath furnace



f and the like,

i' refractory walls of "alumina 'and silica mixed in 5 Patented Nov. 24, 1942 i lWarren F. Heineman, Milwaukee, Wis.; to A. osmmi corporation, Milwaukee, wis., :s

`corporation of New York *I Application May 1, 1941, Serial No. 391,233

y invention relates to salt bath furnaces employing molten liquid as the heating means.

Such furnaces are generally constructed with suitable proportions and the vsalt is generally barium chloride or some other suitable material which is. conductiveI to electricity when molten. The salt is usually heated or kept molten by meansV of electricityfpassing through it between suitably spaced electrodes dippink in they bath. and some means are provided to keep the bath in circulation so that it will stay at a more uniform .temperature throughoutand no hot spots will develope in it.v

The articles to be'heated are usually fed along by means of a suitable conveyor and. successively somma (01.26644) tional viewv of the furnace showing the floating top, the conveyor, and the tubes being heated;

Fig. 2 is a top plan view of one end of the sectionfand p Fig. 3 is a transverse vert the furnace.

- furnace. the tubes being heated being shown in al section through The walls l of therumac'e.' as wen as its bottom, are made up. from or suitably lined `with refractory brick interlocked together in any suitable manner -to provide a containerfor the salt 2. Suitable groups of electrodes 3 are suspended in the salt to supply the heating current thereto.

These maybe of any standard construction. and thefelect-rodes in each group are usually spaced rather closely to provide a stirring action for the dipped or submerged in the bath for heating.

The length of the bath isdependent upon the rate of'movement of articles along the conveyor and the time required for heating each article to the desired temperature.-

In certain instances it has become desirable to heat vertically suspended tubular articles at the lower end only* andto have a very sharp line of heat gradient from the heated portion to the relatively cold'portion. Heretofore, with the construction of saltbath furnaces it has been impossible to obtain the necessary sharp line of heat gradient due either' to the radiant heat coming upwardly from the bath or to the reflection of radiant heat by the furnace tile at vthe top of the furnace.

The present invention has as its object to prevent radiant heat at the top of the bath ,and thereby enable thetubesto be heated substanf tially solely by conduction from the salt bath. Such heating can be carriedon sumciently rapid .to provide a very narrow'band of heat gradient between thev heatedfllo'wer end of the tube and the upper cold portidjn of the tube.

In accordance with' the invention the bath is l covered vby refractory material preferably in rick form floating on the bath, the brick being preferably tied together and to the side walls of the furnace and being arranged to leave a longitudinal slot in the center for receiving the.,

tubes to be heated and through which the tubes are suspended and along which they travel in being heated.

The invention may be better understood by reference to the accompanying drawing illusirating va preferred embodiment of it and in which:

Figure 1 is a diagrammatic-longitudinal secmolten salt resulting from the action of the current passing between the electrodes. 'I'he electrodes are suspended from the side walls of the ifurnace. The roof 4 f the furnace is flexible and comprises refractory brick l similar to the walls I. but not` rigidly interlocked with one another. The bricks 5 are preferably loosely tied to each other and to the furnace wall l by means ofv special alloy wire 8. The rof 4 is constructed to provide an open slot 'l extending along the longitudinalcenter line for receiving the tubes l or other articles being heated. The conveyor $01 for transporting the tubes I and dipping the same into the bath extends above the slot and parallel to it in the heating zone. The roof has suitable notches at its outer edge for receiving the electrodes 3.

3g In operationof the' furnace the tile or brick l 5o raising floats on the salt bath 2 and being fastened together like a raft and flexibly secured to the side walls', it is'capable of vertical moyement with changes in level `of the salt.v The level of the 40 bath may change with temperature changes or it may change by reason of the dipping of tubes l into it or by reason of a removal of a certain amount of the salt which always sticks on the surface of the tubes 8 as the latter are withdrawn from the bath. The bath is replenished from time to time by adding fresh dry unfused salt.

The raising and lowering of the bath level due to these and other factors merely results in a and lowering of the brick 5 and the latter enectively prevent large losses of radiant heat. The tubes' being heated have their lower ends submerged in the salt bath heated rapid;`7 with a resultant sharp margin betwee'. theheatd and unheated portions.

Instead of separate wires linking the bricks together and to the side walls as shown, the wires C may pass through holes in the several bricks or they may be received in grooves in the tops of the bricks. the ends of the wires being secured tc separate bricks or to the furnace wall. Instead of employing wire, the bricks may be suitably interlocked.

Various embodiments of the invention may be employed within the scope thereof as set forth in the accompanying claims.

The invention is claimed as follows:

1.1n a furnace employing a liquid heating bath, a refractory roof comprising vbricks arranged side by side and iloating on the bath, and means tying said bricks to the wall of the furnace to maintain said bricks in position and provide a central longitudinal opening for the passage of articles into, through and out of theliquid bath.

2. In a furnace employing a liquid heating bath, a refractory roof comprising bricks arranged .side by side and floating on the bath, and

means tying said bricks together'and to the side asesina walls of the furnace in a manner providing for raising and lowering of said bricks with changes in level of the liquid bath and leaving a path between rows of bricks for receiving articles sulpended from an overhead conveyor, which ar` ticles are to be dipped in the bath for heating the same and to be conveyed along said opening.

3. A liquid bath heating furnace for uniformly heating the lower ends of articles suspended therein with a substantially sharp heat radiant between the heated portion and the remaining cold portion of the articles, comprising a iiuld type refractory furnace pot; a liquid heating bath therein. means to heat said liquid bath, and a refractory roof noating on said bath to prevent heat loss therefrom, said roof having a relatively narrow open slot for receiving the'artlcle being partially suspended in the bath and traveling along said slot, gid noating roof thereby preventing radiation'of heat from the bath to the upper portion of the article disposed above the Same.

WARREN F. 

